Evasion of apoptosis is a hallmark of cancer (Hanahan & Weinberg (2000) Cell 100:57-70). Cancer cells must overcome a continual bombardment by cellular stresses such as DNA damage, oncogene activation, aberrant cell cycle progression and harsh microenvironments that would cause normal cells to undergo apoptosis. One of the primary means by which cancer cells evade apoptosis is by up-regulation of anti-apoptotic proteins of the Bcl-2 family.
Compounds that occupy the BH3 binding groove of Bcl-2 proteins have been described, for example by Bruncko et al. (2007) J. Med. Chem. 50:641-662. These compounds have included N-(4-(4-((4′-chloro-(1,1′-biphenyl)-2-yl)methyl)piperazin-1-yl)benzoyl)-4-(((1R)-3-(dimethylamino)-1-((phenylsulfanyl)methyl)propyl)amino)-3-nitrobenzene-sulfonamide, otherwise known as ABT-737, which has the formula:

ABT-737 binds with high affinity (<1 nM) to proteins of the Bcl-2 family (specifically Bcl-2, Bcl-XL and Bcl-w). It exhibits single-agent activity against small-cell lung cancer (SCLC) and lymphoid malignancies, and potentiates pro-apoptotic effects of other chemotherapeutic agents. ABT-737 and related compounds, and methods to make such compounds, are disclosed in U.S. Patent Application Publication No. 2007/0072860 of Bruncko et al.
More recently, a further series of compounds has been identified having high binding affinity to Bcl-2 family proteins. These compounds, and methods to make them, are disclosed in U.S. Patent Application Publication No. 2007/0027135 of Bruncko et al. (herein “the '135 publication”), incorporated by reference herein in its entirety, and can be seen from their formula (Formula I below) to be structurally related to ABT-737.
In compounds of Formula I:
X3 is chloro or fluoro; and                (1) X4 is azepan-1-yl, morpholin-4-yl, 1,4-oxazepan-4-yl, pyrrolidin-1-yl, N(CH3)2, N(CH3)(CH(CH3)2), 7-azabicyclo[2.2.1]heptan-1-yl or 2-oxa-5-azabicyclo[2.2.1]hept-5-yl; and R0 is        

where
X5 is CH2, C(CH3)2 or CH2CH2;
X6 and X7 are both hydrogen or both methyl; and
X8 is fluoro, chloro, bromo or iodo; or                (2) X4 is azepan-1-yl, morpholin-4-yl, pyrrolidin-1-yl, N(CH3)(CH(CH3)2) or 7-azabicyclo[2.2.1]heptan-1-yl; and R0 is        

where X6, X7 and X8 are as above; or                (3) X4 is morpholin-4-yl or N(CH3)2; and R0 is        

where X8 is as above.
The '135 publication states that while inhibitors of Bcl-2 family proteins previously known may have either potent cellular efficacy or high systemic exposure after oral administration, they do not possess both properties. A typical measure of cellular efficacy of a compound is the concentration eliciting 50% cellular effect (EC50). A typical measure of systemic exposure after oral administration of a compound is the area under the curve (AUC) resulting from graphing plasma concentration of the compound versus time from oral administration. Previously known compounds, it is stated in the '135 publication, have a low AUC/EC50 ratio, meaning that they are not orally efficacious. Compounds of Formula I, by contrast, are stated to demonstrate enhanced properties with respect to cellular efficacy and systemic exposure after oral administration, resulting in a AUC/EC50 ratio significantly higher than that of previously known compounds.
One compound, identified as “Example 1” in the '135 publication, is N-(4-(4-((2-(4-chlorophenyl)-5,5-dimethyl-1-cyclohex-1-en-1-yl)methyl)piperazin-1-yl)benzoyl)-4-(((1R)-3-(morpholin-4-yl)-1-((phenyl sulfanyl)methyl)propyl)amino-3-((trifluoromethyl) sulfonyl)benzenesulfonamide, otherwise known as ABT-263. This compound has a molecular weight of 974.6 g/mol and has the formula:

ABT-263 binds with high affinity (<1 nM) to Bcl-2 and Bcl-XL and is believed to have similarly high affinity for Bcl-w. Its AUC/EC50 ratio is reported in the '135 publication as 56, more than an order of magnitude greater than that reported for ABT-737 (4.5). For determination of AUC according to the '135 publication, each compound was administered to rats in a single 5 mg/kg dose by oral gavage as a 2 mg/ml solution in a vehicle of 10% DMSO (dimethyl sulfoxide) in PEG-400 (polyethylene glycol of average molecular weight about 400).
Oral bioavailability (as expressed, for example, by AUC after oral administration as a percentage of AUC after intravenous administration) is not reported in the '135 publication, but can be concluded therefrom to be substantially greater for ABT-263 than for ABT-737. However, further improvement in oral bioavailability would be advantageous. Various solutions to the challenge of low oral bioavailability have been proposed in the art. For example, U.S. Pat. No. 5,645,856 to Lacy et al. proposes formulating a hydrophobic drug with (a) an oil, (b) a hydrophilic surfactant and (c) a lipophilic surfactant that substantially reduces an inhibitory effect of the hydrophilic surfactant on in vivo lipolysis of the oil, such lipolysis being said to be a factor promoting bioavailability of the drug. Among numerous classes of hydrophilic surfactants listed are phospholipids such as lecithins.
U.S. Pat. No. 6,267,985 to Chen & Patel is directed, inter alia, to a pharmaceutical composition comprising (a) a triglyceride, (b) a carrier comprising at least two surfactants, one of which is hydrophilic, and (c) a therapeutic agent capable of being solubilized in the triglyceride, the carrier or both. It is specified therein that the triglyceride and the surfactants must be present in amounts providing a clear aqueous dispersion when the composition is mixed with an aqueous solution under defined conditions. Among extensive separate lists of exemplary ingredients, mention is made of “glyceryl tricaprylate/caprate” as a triglyceride, and phospholipids including phosphatidylcholine as surfactants.
U.S. Pat. No. 6,451,339 to Patel & Chen mentions disadvantages of presence of triglycerides in such compositions, and proposes otherwise similar compositions that are substantially free of triglycerides, but that likewise provide clear aqueous dispersions.
U.S. Pat. No. 6,309,663 to Patel & Chen proposes pharmaceutical compositions comprising a combination of surfactants said to enhance bioabsorption of a hydrophilic therapeutic agent. Phospholipids such as phosphatidylcholine are again listed among exemplary surfactants.
U.S. Pat. No. 6,464,987 to Fanara et al. proposes a fluid pharmaceutical composition comprising an active substance, 3% to 55% by weight of phospholipid, 16% to 72% by weight of solvent, and 4% to 52% by weight of fatty acid. Compositions comprising Phosal 50 PG™ (primarily comprising phosphatidylcholine and propylene glycol), in some cases together with Phosal 53 MCT™ (primarily comprising phosphatidylcholine and medium chain triglycerides), are specifically exemplified. Such compositions are said to have the property of gelling instantaneously in presence of an aqueous phase and to allow controlled release of the active substance.
U.S. Pat. No. 5,538,737 to Leonard et al. proposes a capsule containing a water-in-oil emulsion wherein a water-soluble drug salt is dissolved in the water phase of the emulsion and wherein the oil phase comprises an oil and an emulsifying agent. Among oils mentioned are medium chain triglycerides; among emulsifying agents mentioned are phospholipids such as phosphatidylcholine. Phosal 53 MCT™, which contains phosphatidylcholine and medium chain triglycerides, is reportedly used according to various examples therein.
U.S. Pat. No. 5,536,729 to Waranis & Leonard proposes an oral formulation comprising rapamycin, at a concentration of about 0.1 to about 50 mg/ml, in a carrier comprising a phospholipid solution. It is stated therein that a preferred formulation can be made using Phosal 50 PG™ as the phospholipid solution. An alternative phospholipid solution mentioned is Phosal 50 MCT™.
U.S. Pat. No. 5,559,121 to Harrison et al. proposes an oral formulation comprising rapamycin, at a concentration of about 0.1 to about 100 mg/ml, in a carrier comprising N,N-dimethylacetamide and a phospholipid solution. Examples of the more preferred embodiments are shown to be prepared using Phosal 50 PG™. An alternative phospholipid solution mentioned is Phosal 50 MCT™.
U.S. Patent Application Publication No. 2007/0104780 of Lipari et al. discloses that a small-molecule drug (defined therein as having molecular weight, excluding counterions in the case of salts, not greater than about 750 g/mol, typically not greater than about 500 g/mol) having low water solubility can be formulated as a solution in a substantially non-aqueous carrier comprising at least one phospholipid and a pharmaceutically acceptable solubilizing agent. The solution, when mixed with an aqueous phase, is said to form a non-gelling, substantially non-transparent liquid dispersion. Illustratively, formulations of N-(4-(3-amino-1H-indazol-4-yl)phenyl)-N′-(2-fluoro-5-methylphenyl)urea (the protein tyrosine kinase inhibitor ABT-869) comprising Phosal 53 MCT™ and other ingredients are described therein.
Oxidation reactions represent an important degradation pathway of pharmaceuticals, especially when formulated in solution. A large body of information is available on oxidative mechanisms, but relatively few studies have been performed with specific drugs. Hovorka & Schoneich (2001) J. Pharm. Sci. 90:253-269 have stated that this lack of pharmaceutically relevant data leads to poor predictive ability with respect to drug oxidation between manufacture and administration of formulations of oxidizable drugs, and a consequently uninformed, largely empirical utilization of antioxidants in formulations.
Oxidation can occur by a number of pathways, including uncatalyzed autoxidation of a substrate by molecular oxygen, photolytic initiation, hemolytic thermal cleavage, and metal catalysis. Various functional groups show particular sensitivity towards oxidation. In particular, thioethers can degrade via hydrogen abstraction at the α-position to the sulfur atom or by addition of an α-peroxyl radical directly or via a one-electron transfer process, which transforms a sulfide to a sulfine, sulfone, or sulfoxide (Hovorka & Schöneich, supra).
The (phenylsulfanyl)methyl group of compounds of Formula I are seen to have a thioether linkage, which is susceptible to oxidation, for example in presence of oxygen or reactive oxygen species such as superoxide, hydrogen peroxide or hydroxyl radicals. The above-referenced '135 publication includes antioxidants in an extensive list of excipients said to be useful for administering a compound of Formula I.
A particular type of disease for which improved therapies are needed is non-Hodgkin's lymphoma (NHL). NHL is the sixth most prevalent type of new cancer in the U.S. and occurs primarily in patients 60-70 years of age. NHL is not a single disease but a family of related diseases, which are classified on the basis of several characteristics including clinical attributes and histology.
One method of classification places different histological subtypes into two major categories based on natural history of the disease, i.e., whether the disease is indolent or aggressive. In general, indolent subtypes grow slowly and are generally incurable, whereas aggressive subtypes grow rapidly and are potentially curable. Follicular lymphomas are the most common indolent subtype, and diffuse large-cell lymphomas constitute the most common aggressive subtype. The oncoprotein Bcl-2 was originally described in non-Hodgkin's B-cell lymphoma.
Treatment of follicular lymphoma typically consists of biologically-based or combination chemotherapy. Combination therapy with rituximab, cyclophosphamide, doxorubicin, vincristine and prednisone (R-CHOP) is routinely used, as is combination therapy with rituximab, cyclophosphamide, vincristine and prednisone (RCVP). Single-agent therapy with rituximab (targeting CD20, a phosphoprotein uniformly expressed on the surface of B-cells) or fludarabine is also used. Addition of rituximab to chemotherapy regimens can provide improved response rate and increased progression-free survival.
Radioimmunotherapy agents, high-dose chemotherapy and stem cell transplants can be used to treat refractory or relapsed non-Hodgkin's lymphoma. Currently, there is not an approved treatment regimen that produces a cure, and current guidelines recommend that patients be treated in the context of a clinical trial, even in a first-line setting.
First-line treatment of patients with aggressive large B-cell lymphoma typically consists of rituximab, cyclophosphamide, doxorubicin, vincristine and prednisone (R-CHOP), or dose-adjusted etoposide, prednisone, vincristine, cyclophosphamide, doxorubicin and rituximab (DA-EPOCH-R).
Most lymphomas respond initially to any one of these therapies, but tumors typically recur and eventually become refractory. As the number of regimens patients receive increases, the more chemotherapy-resistant the disease becomes. Average response to first-line therapy is approximately 75%, 60% to second-line, 50% to third-line, and about 35-40% to fourth-line therapy. Response rates approaching 20% with a single agent in a multiple relapsed setting are considered positive and warrant further study.
Current chemotherapeutic agents elicit their antitumor response by inducing apoptosis through a variety of mechanisms. However, many tumors ultimately become resistant to these agents. Bcl-2 and Bcl-XL have been shown to confer chemotherapy resistance in short-term survival assays in vitro and, more recently, in vivo. This suggests that if improved therapies aimed at suppressing the function of Bcl-2 and Bcl-XL can be developed, such chemotherapy-resistance could be successfully overcome.
Apoptosis-promoting drugs that target Bcl-2 family proteins such as Bcl-2 and Bcl-XL are best administered according to a regimen that provides continual, for example daily, replenishment of the plasma concentration, to maintain the concentration in a therapeutically effective range. This can be achieved by daily parenteral, e.g., intravenous (i.v.) or intraperitoneal (i.p.) administration. However, daily parenteral administration is often not practical in a clinical setting, particularly for outpatients. To enhance clinical utility of an apoptosis-promoting agent, for example as a chemotherapeutic in cancer patients, a dosage form with good oral bioavailability would be highly desirable. Such a dosage form, and a regimen for oral administration thereof, would represent an important advance in treatment of many types of cancer, including non-Hodgkin's lymphoma, and would more readily enable combination therapies with other chemotherapeutics.
It would be even more desirable to prepare such a dosage form wherein rate of oxidative degradation, particularly at the sulfur atom of the (phenylsulfanyl)methyl group of a compound of Formula I, is decreased, permitting acceptable storage stability and shelf-life of the dosage form.